Most in-shot burners found in the prior art have an overall length of five inches or more. The term overall length as herein used, refers to the axial length of the burner assembly as measured over the spud holder located at the input end of the burner and the flame retainer housing located at the output end of the burner. Attempts to reduce the length of in-shot burners used in gas furnaces and, in particular, non-condensing multi-poise furnaces, have resulted in a reduction in burner performance primarily because the shorter burners generally can not effectively draw in sufficient primary air to optimally support combustion. In addition, shorter burners found in the prior art do not provide good fuel and air mixing or the stable burning characteristics needed to avoid pulsation, blow-off and flashback in the burner. Shorter burners are highly desirous in multi-poised furnaces which are designed to operate not only in an upright position, but also when lying on one side or the other or in an inverted position. By shortening the burner section inside the casing, sufficient room can be gained to permit the flue pipe to be repositioned internally to accommodate any of the multiple furnace positions.
Additionally, it has been found that short burners can be readily formed in multiple burner units using well known plate stamping techniques. The burner units can be fabricated containing different numbers to accommodate various size furnaces. The units are easy to install and are not only space saving, but also cost effective.